High frequency amplifier



March 22, 1932. 5 G l Y 1,850,784

HIGH FREQUENCY AMPLIFIER Filed Sept. 7, 1929 @nmwv'u, Mama] ram Xciorrzeya Patented Mar. 22, 1932 i UNETEQ P n-i s NT. citric CHRISTOPHER 1 EDMUND GERVASE BAILEY, OF, 'LONDON, ENGLAND, .ASSIGNOR, BY

MESNE ASSIGNMENTS, TO RADIO CORPORATION OF AMERIGA OF NEW YORK, N. Y.,]'

A CORPORATIONS OF DELAWARE HIGH-FREQUENCY1 AMPLIFIER Application filed September 7, 1929, Serial No. 391,018, and in Great Britain September 27, 1928. i

The present invention relates to high frequency amplifiers. It is well known that when the selectivity of a high'frequency amplifier for use in the amplification "of wireless telephony signals is madesufiiciently great to eliminate unwanted signals, the amplification at frequencies onboth sides of the carrier frequency is less than that at the'carrier frequency itself and decreases rapidly asthe difierence from the carrier frequency in.- creases. Assuming that, for the satisfactory reproduction of music or speech,-frequencies from 25 to 10,000 cycles per second are required to be received with sensibly equal intensity, it is necessary that the'high frequency amplifier should amplify equally all frequencies lying between N10,000 and N+ 10,000 cycles per second where N is the carrier frequency.

As the selectivity of the amplifier is increased the higher audio frequencies are cut out altogether and the intermediate frequen cies are less amplified than the low frequencies with consequent ill effect upon the quaL ity of the reproduced sounds.

The present invention is concerned with improved circuit arrangements whereby the above effects can be reduced. According to the presentinvention a circuit arrangement. for amplifying modulated high frequency carrier oscillations comprises two circuits tuned to the carrier frequency to be amphfied,'one of said circuits being adapted to re-i duce, in effect, the amplification of the circuit arrangement over a band of frequencies on either side oflsaid carrierfrequency. The

latter circuit is less heavily damped than the other circuit. v

The invention will be described'by way of example, with reference to the accompanyingdrawing, as applied to a high frequency amplifier. in which the anode circuit it tuned. The valve V is a high frequency amplifier having input terminals 1 which may be con nected to the receiving aerial circuit. In the anode circuit of the valve V is a tuned cir- I cuit 2, the anode current being fed to this valve through the inductance coil of this tuned circuit. The anode of thevalve V is connected-to the grid of the valve V which may be a detector valve, throughan inductance 3 and a condenser 4. An inductance 5 is closely coupled to the inductance 3 and a variable condenser 6 is connected' in' parallel wlth the two inductances 3 and 5 in series.

It is essential that some resistanceshouldbe provided in the circuit, 8, 5, 6 and it is sometimes found necessary to add a small series, resistance 7 The damping of this circuit 3,

carrierto be received, and if the values of the components of these circuitshave been suitably selected the overall. amplificationv for any givendegree of selectivity will be found to be much more uniform over the important frequency hand than would b'ethe case if the second tuned circuit. between the anode of one valveand the grid of the next, were not included. The effect of thistuned circuit" isv 'to reduce the amplification of the frequencies in the neighborhood of the carrier frequency r in relation to the amplification. offthefre quencies further from the carrier frequency. 7

It will be understood that the invention is not 1i mited to the case in which a tunedanode circuit is used, the invention being applicable to circuits embodvlng other forms of conplings, for example. high frequency, trans: former. coupling. The controls ofthe two A condensers may if desired be mechanically coupled in order toensure that thetwo tuned circuits arealways tuned to the same frequencvbut preferably. however, the circuit is' used as an intermediatecircuit amplifier 1113 super-heterodyne receiver n whichi'the intermediate frequency is fixed and theheterodyne fre uency lSI/Tflllilbl, In-such a circuitthe adjustmentof the two-condensers can be made once and for all and the selec tivity and the shape of the amplification curve will then remain constant whatever the frequency of the carrier wave to be received may be.

I-claim: Y i

1. A circuit arrangement for amplifying,

modulated high frequency carrier oscillations comprising two circuits tuned to the carrier frequency to be amplified and arranged successively to receive said oscilla- 5 tions, the second one of said circuits being damped whereby it is adapted to reduce in effect the amplification of the circuit arrangement over a band of frequencies on either side of said carrier frequency, and the first of said circuits being damped to a greater degree than the second one of said circuits.

2. A circuit arrangement for amplifying modulated high frequency carrier oscilla- .tions including two thermionic valves each having an anode circuit and a grid circuit, two circuits tuned to the carrier frequency to be amplified, one of said circuits being disposed in parallel with the anode circuit of one of said thermionic valves and being thereby damped, the other of said circuits including a damping resistance providing a lesser degree of damping than that applied to said parallel circuit and further including two closely coupled inductances one of which is disposed in series between the anode circuit of said one of said valves and the grid circuit of the other of said valves.

7 3. Ina high frequency amplifier, the combination of a tuned circuit, a thermionic valve connected therewith whereby said circuit is damped, a second tuned circuit, said circuit including an inductance and means for damping said circuit to a less degree than the first named circuit, a second inductance in said second named circuit closely coupled with the first named inductance, and a sec- .ond thermionic,valve'having a grid connected with said circuit at a point between said I indnctanoes. 1 4. In a high frequency amplifien'the combination of a tuned circuit responsive to a predetermined frequency, a thermionic valve aving an anode connected with said circuit whereby said circuit is damped, a second tuned circuit responsive to said predetermined frequency, said circuit including an inductance and resistance having a value such that said circuit is clamped to a less degree than the first named circuit, a second inductance in said second named circuit closely coupled with the first named inductance, a thermionic valve having a grid, and means providing a connection from said first named -circuit through said first named inductance with the said grid. 7 In testimony whereof I have signed my name to thisspecification.

CHRISTOPHER EDMUND GERVASE BAILEY. 

